I've had similar issues before. Could be rebound prolactin from "too much" sex recently (this is a pure guess, I've only had an issue from that when it was several times in the same day). You don't mention an AI, what/how much are you taking? Estrogen too high or even too low can cause limp noodle (I actually had issues from crashing my E while on TRT dose, turns out after a while on TRT you don't need an AI).
Biggest possibility is it was all in your head. Stress is one of the biggest (if not the biggest) contributors to ED. If she is so hot you almost feel lucky to bag her or like she's out of your league and feel pressured to perform and impress her, then you could be causing your own problem.
I used primo (700mg/week, UGL) last year and had no issues but like you mentioned, could be fake. Had some bad ED on tren (19 nor and all), but not on deca when I used it years ago with a large dose sust cycle (really dumb cycle, I'm probably lucky I can get it up let alone have fathered two kids).
If you've had an insane libido spike and this ED just popped up several weeks in, I'd chalk it up to stress. I don't know anything about RAD-140 or sarms in general, so I can't comment on that one.